Mark some internal sealed trait @DoNotInherit

[He-Pin]

There are classes is not marked with @DoNotInherent, then Java user may extends that classes. We should mark it with @DoNotInherent.

And there are some classes should be annotated with @InternalApi.

refs: apache/pekko-connectors#588

[mdedetrich]

Is @DoNotInherent necessary if the class is final, that is already implied?

Typically @ DoNotInherent is used for classes which can be extended but only for private cases

[He-Pin]

no, I mean we should mark on sealed trait and sealed abstract class

[mdedetrich]

no, I mean we should mark on sealed trait and sealed abstract class

That makes perfect sense, :+1 from me